Dosage compensation and its roles in evolution of sex chromosomes and phenotypic dimorphism: lessons from Drosophila, C.elegans and mammals

Abstract

In many sexually reproducing species, sex is determined by cytologically distinguishable ‘sex chromosomes’. The popular view is that the consequence of heteromorphic sex chromosomes is detrimental, and evolutionary emergence of dosage compensation mechanism is expected for two fold upregulation of X linked genes in order to restore the balance for the haplo-X in the sex against the diplo X of the other. Since, male and female share nearly identical genome in most animals, and since antagonistic selection operate for the expression divergence of the sex biased genes between sexes for mating type distinction, dosage compensation system is evolved in many species to link global transcription profile of the genome through histone variants and epigenetic modification of the genes for driving sex determination function. Whole genome transcriptome analyses and the investigations on the profiling of accessible chromatin components in male and female at different phase of development of Drosophila, C. elegans and mammal revealed that 50–60% X and autosomal genes of the genomes are expressed under sex specific selection through allelic bias (except some required dosage sensitive genes) expression, ranging from absent to complete compensation. The review focuses the recent development of dosage compensation research and illustrates its roles in sex chromosome evolution and sexual dimorphism in Drosophila, C. elegans and mammals.

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